A lot of algebra problems, a little time to do them!

Hi everybody!

I have few problems that needs to be solve by to tomorrow!!! Some of the problems are quite easy, but I just don't seem to get the right answers.

Here are the problems:

1) (x-y)(x+y)-(x-y)^2-(x+y)^2

2) 2/5x^2 - 5/2x(x-2)-3x

3) (x+4)^2 / x^2-16

4) 3a/4 + 1/4b(b-a/b) + 1/2b^2

5) x^2+2x-35 < 0

6) x-2y+3z=4

3x+2y-4z=10

x+y+z=9

7) x+y= -1

x*y= -6

8) Let Y be the number of units of a product and let p be the price per unit of the same product. One of the equations below describes the correspondence between the demand for the product and the price per unit. The other equation describes the correspondence between the supply and the price per unit.

Y=900-100p

Y=300+50p

a) Which of the equations describes the demand situation and which describes the supply situation? Explain why.

b) Draw the graph of the two equations in the same coordinate system.

c) Solve the equation system both graphically and algebraically.

I know theres a lot of question, but I'll appreciate if you could help!

Thank you!!